In a cellular wireless network (for example a small cell wireless network), downlink (DL) interference has an impact on the uplink (UL) SINR (Signal-to-Interference-Noise-Ratio) of the user equipment (UE) if the station randomly chooses transmission directions. The impact is more significant between UP-DL (uplink-downlink) communications between the stations and the UEs in a small wireless network.
Taking the LTE TDD for example, one of the advantages of using LTE TDD is that it is possible to dynamically change the uplink and downlink balance and characteristics to meet the load conditions. In order that this can be achieved in an ordered fashion, a number of standard configurations have been set within the LTE standards.
In LTE TDD subframe allocation, a total of seven UP-DL (uplink-downlink) configurations have been set, and these use either 5 ms (microsecond) or 10 ms switch-point periodicities. In the case of the 5 ms switch-point periodicity, a special subframe exists in both half frames. In the case of the 10 ms switch-point periodicity, the special subframe exists in the first half frame only.
Please refer to FIG. 1A and FIG. 1B. In FIG. 1A, a Pico station chooses a UL-DL configuration according to its UL-DL traffic conditions based on the table shown in FIG. 1B. FIG. 1B shows the seven configurations of 3GPP Long Term Evolution (LTE) TDD UL-DL configurations. Different Pico stations 110˜150 have chosen their respective UL-DL configurations, for example, the Pico Stations 110, 120, 130, 140, 150 respectively chooses UL-DL configurations 0, 3, 6, 1 and 5. The information for every configuration is respectively shown in FIG. 1B, in which DL-to-UL switch-point periodicities are 5 ms or 10 ms, and subframes 0˜9 are configured as shown in the table of FIG. 1B. In the table, “D” is a subframe for downlink transmission, “S” is a special subframe used for a guard time, and “U” is a subframe for uplink transmission.
When the Pico station 120 with Configuration 3 has DL transmission in the subframes 7 and 8, it may cause a severe interference to the neighbor Pico station 110 with Configuration 0 to receive an UL signal in the subframes 7 and 8. It is observed that an UL SINR of the UE is suffered severer DL interference from the neighbor Pico stations, if both they are active in transmission and choose different configurations.